Mammography is currently the most effective screening and diagnostic tool for early detection of breast cancer, and has been attributed to the recent reduction of breast cancer mortality rate. However, the nature of the two-dimensional mammogram makes it difficult to distinguish a cancer from overlying breast tissues, and the interpretation can be variable among radiologists. A higher rate of false positive and false-negative test results exist because the dense tissues interfere with the identification of abnormalities associated with tumors. Digital breast tomosynthesis (DBT) is a three-dimensional imaging technique that is designed to overcome this problem. It is a limited angle tomography technique that provides reconstruction planes in the breast using projection images from a limited angular range.
Several prototype DBT scanners have been manufactured by commercial vendors. The system designs are based on a full-field digital mammography (FFDM) unit. A mammography x-ray tube is used to collect the projection images by moving 10-50 degrees around the object. The reported total scanning time is 7-40 seconds depending on the number of views and the thickness of the breast, which is much longer than that of the regular mammography. The long imaging time can cause patient motion blur which degrades image quality and can make patients uncomfortable. Further, the power of the x-ray source, gantry rotating speed and detector frame rate limit the scanning speed of the current DBT systems.
DBT systems utilize the standard mammography x-ray tube with about a 300 μm x-ray focal spot size. Due to the gantry rotation and mechanical instability, the effective focal spot size during image acquisition is larger than the static value which degrades the image resolution. Two gantry rotation modes have been developed. One commercially-available system uses a stop-and-shoot technique. The gantry makes a full stop before taking each projection image. Acceleration/deceleration can cause mechanical instability of the system. A continuous rotation mode is used in other commercially available systems. The gantry keeps a constant rotation speed during the whole imaging process. In this case, the x-ray focal spot size is enlarged along the motion direction. The value of the enlargement depends on the rotation speed and the exposure time. It has been reported that the x-ray focal spot moves about 1 mm in a typical scan. This does not leave room for further reduction of the total scanning time, which will require a faster gantry rotation and a larger focal spot blurring.
It would be beneficial to provide x-ray imaging systems and methods having reduced data collection times and improvements for patient comfort. One or more such improvements can enable new applications for x-ray imaging of breast tissue as well as other objects. Accordingly, it is desirable to provide x-ray imaging systems and methods having one or more of these improvements.
In addition, current clinical mammography scanners use polychromatic x-ray radiation with slight energy filtering. It is known that monochromatic and quasi-monochromatic radiation provides better imaging quality and can potentially reduce the imaging dose. Currently, there is no effective way, however, to generate monochromatic or quasi-monochromatic radiation in a clinical environment that can provide sufficient x-ray photo flux. Accordingly, it is desirable to provide x-ray imaging systems and methods that can perform monochromatic or quasi-monochromatic imaging in a clinically acceptable scanning speed.